Premature hatching associated with climate change may lead to depletion of fish stocks

Tiistai 15.10.2024 klo 17.47 - Mikko Nikinmaa

Cowan et al. reviewed premature hatching of fish embryos in climate change scenario in Global Change Biology (DOI: 10.1111/gcb.17488). Virtually all anthropogenic changes in aquatic environment trigger premature hatching: temperature increase, hypoxia, acidification and increase of water carbon dioxide content, presence of pathogens, metal pollution and organic pollutants.

Simplified, hatching starts to occur, when the oxygenation level of the embryo decreases below a setpoint. This triggers the secretion of choriolytic enzymes, which enables the embryo to break the egg surface and become a fry. In the case of increased temperature, small increases can be tolerated, as, although temperature increase increases the oxygen consumption of the embryo, it also speeds up development and thus the embryo is adequately developed when the hatching program sets on earlier than at lower temperatures. However, too fast and pronounced increase in temperature leads to a decrease in embryonal oxygen level, which triggers hatching, before the embryo is adequately developed. In such a case, mortality at hatch and during the early life of the fry is increased. In hypoxic conditions, the oxygen level triggering hatching is often reached before the embryo is adequately developed for normal life, causing increased egg and fry mortality. Several pollutants and infections also affect the oxygen consumption of the embryo in such a way that development at hatch is not optimal for successful later life.

Although optimal oxygen level of the embryo at hatch is the most important factor affecting fry recruitment, virtually no fisheries estimations/predictions take that into account. Stock recruitment is still based mainly on catch statistics, although such metrics cannot take into account anything that affects egg and fry development. Yet, early development of fish is the major driver of future fish stocks.